Testing circuits for group selectors in automatic systems



Feb. 26 1952 T A. MAMOR 2,586,838

TESTING CIRCUITS FOR GROUP SELECTOR-S IN AUTOMATIC SYSTEMS Filed April 19, 1947 A INVENTOR A RMAN D MAM O R ATTQRNEY Patented Feb. 26, 1952 TESTING CIRCUITS FOR GROUP SELECTORS IN AUTOMATIC SYSTEMS Armand Mamor, Antwerp, Belgium, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application April 19, 1947, Serial No. 742,574 In the Netherlands January 30, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires January 30, 1966 3 Claims. (Cl. 179-18) The present invention relates to a test circuit for automatic telephone selectors or similar systems for establishing connections, in which the testing of contacts takes place over a separate test brush.

In these systems it may happen that the brush carriage of the selector overshoots the tested terminal and stops between two outlets. This may result from either late testing on an outlet just becoming free at the moment a, hunting group selector passes or it may be caused by a double test resulting in a delayed operation of the test relay.

Such a failure may result in the loss of a call and/or in a hang-up of the circuits involved.

The present invention overcomes these disadvantages because the operating circuit of the test relay includes an interrupter segment, the contact making portions of which are grounded for at least part of the time when the test terminals are engaged by the test brush.

The invention will be described with reference to the accompanying drawing, in which Fig. 1 is a circuit diagram of an embodiment; and

Fig. 2 is a chart of the engagement times of the interrupter segment and the test terminals.

In the circuit arrangement of Fig. 1 the operating circuit of test relay l is controlled via an interrupter segment 2 arranged so that at the beginning of the time during which a test terminal 3 of a trunk line engages testing brush 4 wiper 5 grounds interrupter segment 2. The amount of time during which wiper 5 and terminal 3 are simultaneously engaged may vary but is preferably slightly less than half the total engagement time between terminal 3 and brush 4.

This has been schematically represented in Fig. 2 by a time chart in which B indicates the total amount of time during which brush 4 contacts terminal 3, and A indicates that portion of time B during which wiper 5 simultaneously contacts interrupter segment 2. Test relay I may, therefore, operate only during period A (battery, terminal 3, brush 4, high resistance winding relay l, interrupter 2, wiper 5, ground).

As shown in Fig. 1, when interrupter 2 is not connected in the circuit, some means such as a power magnet controlled by a relay 6 moves the brush carriage carrying brush 4 and wiper 5 relative to the terminals and the interrupter segment respectively. A circuit through the high resistance winding of test relay I operates relay I when brush 4 contacts terminal 3 simultaneous with wiper 5s engagement of interrupter segment 2 (battery, terminal 3, brush 4, high resistance winding, relay I, interrupter segment 2, grounded wiper 5). Relay 1 is locked up over its low resistance winding once it has operated over a circuit including a front contact and grounded armature Fig. 2 shows wiper 5 and test brush 4 situated on the brush carriage l in overlapping relationship, so that wiper 5 grounds interrupter 2 from just before the time that test brush 4 engages terminal 3 until just before the brush reaches the middle of terminal 3, thereby assuring that the brush carriage will be stopped, if terminal 3 is found to be idle, and brush 4 will be centered on terminal 3. Overshooting or undershooting of the brush carriage is thus practically eliminated.

A late test is not only avoided, but the number of double tests is also considerably reduced. The majority of such double tests are due to the fact that two or more brushes pass over an outlet just becoming free.

This kind of double test can at present happen during the full length of the closure of the test brush. By reducing the testing period itself, the number of double tests is reduced in the same proportion.

The invention is in no way restricted to the shown embodiment of a local group selector,

but equally applies to all kinds of group selectors.

What I claim is:

1. In a telephone system having an automatic selector in which a plurality of test terminals are engaged selectively by a test brush, and in which the selector is also provided with an interrupter operated thereby, the combination comprising a test relay, an operating circuit for said relay jointly controlled by said test brush and said interrupter and effective to initiate the operation of said test relay only while said test brush engages a selected terminal and the interrupter is closed, a locking circuit for said test relay including said test brush and selected terminal, said locking circuit having less resistance than said operating circuit and being in shunt with said interrupter, means controlled by said test relay for closing said locking circuit, whereby the current through said test brush and selected terminal is increased when said locking circuit is closed, and means also controlled by said test relay for stopping the operation of said selector.

2. In a telephone system, the combination, according to claim 1, in which the interrupter 3 is closed at the beginning of the time during which the test brush engages a test terminal.

3. In a telephone system, the combination, according to claim 1, in which the test relay has a high resistance winding and a low resistance winding connected together and a grounded armature with a front contact, the operating circuit jointly controlled by the test brush and the interrupter including said high resistance winding, and the locking circuit including the low resistance winding and said front contact.

ARMAND MAMOR.

4 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

